RET(ILOC,1)=d*DEXP(exvar)
and exvar = c/kb (d is very small value)
kb is boltzman constant so it has very small value and c is constant
when i apply this UDF in cfx, solver shows error message that Zero divide . But it is not zero.
i annouced exvar and kb as double precision

when i made
RET(ILOC,1)=DSQRT(exvar)
it also shows same error, so i changed
exvar = kb/c
RET(ILOC,1)=1/DSQRT(exvar)
and it works.
but DEXP is not the case. i cannot change that
how can i get result?